The invention involves an air bag module for use preferably in a motor vehicle.
Air bags have been used for a long time as a passive restraint system in motor vehicles. Known modules customarily have a gas generator which instantaneously conducts gas into an air bag upon a trigger signal. The air bag has an air outlet opening, through which the gas flows out of the air bag after a holding time in the air bag. The trigger signal is customarily generated by a crash sensor.
Air bags which are ready for operation are folded together in a capsule. If the gas generator is then activated, gas flows into the air bag, which consequently bursts the capsule, whereupon the air bag is blown up by the gas to full size, in order to protect the vehicle passengers from the consequences of a crash for a certain period of time, 30 ms for example. After reaching the maximum internal pressure in the air bag, the gas escapes through the air outlet opening.
Fundamentally, the known air bag modules address the problem of creating, within a very short period of time, a high enough internal gas pressure in the air bag to soften a submersion of the body parts of the vehicle passengers. In known modules, however, the situation can occur where the body parts are already submerged in the air bag, when the internal pressure built up is not yet high enough to completely unfold the cushioning effect.
This problem is made clear using the two drawing FIGS. 1 and 2.
FIG. 1 shows a known air bag 1, which is equipped with a mounting plate 2 for a gas generator (not shown). The gas generator is connected to the inlet nozzles 3, through which gas flows into the interior of the air bag 1 upon activation. The air bag is equipped with an air outlet opening or vent hole 4, which is always open.
The temporal behavior of this known air bag can be modelled using the temporal progression of the internal pressure P in the air bag 1 according to FIG. 2.
The air bag 1 is--as already mentioned--folded in a capsule, saving space, in the ready-to-operate condition. At the point in time t=0, the gas generator is set off and gas flows into the air bag 1, whereupon the internal pressure of the gas in the air bag instantaneously increases.
As already explained, the air outlet opening 4 is continuously open, i.e. gas flows out of the opening 4 even during the filling operation, so that one may clearly speak of a leakage during the filling operation.
In the progression depicted, the continuous increase of the internal pressure in the air bag deviates from the standard progression (depicted in dashed lines) starting at the time point t.sub.2 and increases super-proportionally. This symbolizes the contact with the body of the vehicle passengers, whereby the air bag volume is for a short time reduced by the pressing in, so that as a result, the pressure is increased for a short time, in comparison with the standard undisturbed progression.
The time point t.sub.2 and the internal pressure built up already in the air bag are the two critical values. If the body contact were to occur earlier than at time point t.sub.2, not enough gas would yet have flowed into the interior of the air bag, in order to be able to provide a cushioning effect by the pressure already built up. This is attributable to the leakage, acting from the beginning, due to the air outlet opening 4.